1. Field of the Invention
The present invention relates to a control device for use in a camera, and more particularly to a control device which controls both the focusing operation of an objective lens of the camera and exposure operation of the camera.
2. Description of the Prior Art
There has been proposed, in U.S. Pat. No. 4,423,936, a control device in which distance detection for the focusing operation and a light measuring for the exposure operation are performed with respect to a plurality of regions in an object area to be photographed, and a distance is selected among the detected distances for the focusing operation. If the selected distance is detected with respect to a single region, a light measurement value measured with respect to the single region is used for exposure operation to control exposure value. On the other hand, if the selected distance is detected with respect to plural regions, plural light measurement values measured with respect to the detected regions are averaged to be used for the exposure operation to control exposure value.
However, in the conventional device as described above, since a primary object to be focused is not always positioned at the detected plural regions, the possibility for obtaining proper exposure for the primary object is relatively low.
Furthermore, in the conventional device, backlight condition is detected in the case that, difference between a first light measurement value measured with respect to the region in which the selected distance is detected and a second light measurement value calculated by averaging all of other light measurement values, is over a predetermined value. Here, if the selected distance is detected with respect to plural regions, the first light measurement value is calculated by averaging plural light measurement values of the plural regions. However, the difference is not always indicating whether the backlight condition or not in the latter case. Fore example, if the selected distance is detected in two regions arranged symmetrically with an optical axis of the objective lens, it is impossible to judge at which region a primary object is positioned in the device. In such case, it would be improper to detect the backlight condition.
There has been proposed, in Japanese Laid-Open patent application No. 60-129732, another control device in which a common ligh receiving device is used for the light measuring and for the distance detection. In the device, one calculating circuit for distance detection and the other calculating circuit for light measuring are provided, and the output of the common light receiving device is sent to two calculating circuits in time-sharing manner or in time-dividing manner. The distance detection calculation and exposure calculation are performed in respective circuits. However, such device has disadvantages that the construction thereof becomes comples since two calculating circuits and switching circuit for selectively transmitting the output of the light receiving device to the two calculating circuits are necessary, and that the operation of the entire device becomes complex since switching operation of the switching means is necessary.